1. Field of the Invention
The present invention relates to electronic circuits for generating mathematical functions, and more specifically to ascending or descending mathematical functions or combinations thereof, and even more specifically, but without limitation thereto, to electronic circuits for generating an output current that is a function of an input voltage, such as an exponential function, using one set of weights, a square function, using another set of weights, or a cubic function, using yet another set of weights.
2. Prior Art
The need for computation of functions such as exponential and trigonometric functions is well-known and documented in the art. There are a multitude of ways to generate the results of such functions for a variety of purposes, all of which are targeted toward a circuit level implementation. Each solution has certain advantages and certain deficiencies that may render a solution not suitable for a specific application. Generally the circuit level implementation can be described as belonging to one of two groups of implementations: digital, i.e., receiving a result through a numerical computation of one sort or another, and analog, i.e., having a circuit generate an output value that is proportionate to an input value in a way that implements the desired mathematical function.
Among the known digital types of solutions are the table lookup methods, polynomial approximation methods, digit-by-digit methods, and rational approximation. An analog circuit is disclosed in U.S. Pat. No. 6,771,111 by Sheng et al. That circuit attempts to use a single stage differential amplifier set-up to provide exponential function circuitry. However, the methods and circuits disclosed by prior art solutions are deficient in at least chip area, speed, or accuracy.
In view of the deficiencies of prior art solutions and in view of the need to provide fast and accurate mathematical functions, for example in wireless communication, it would be advantageous to provide circuits that are capable of providing mathematical functions. It would be further advantageous if such circuits were able to implement several mathematical functions without the need to use different circuit techniques or designs, i.e., be generally dependent on parameters of the circuit, not the circuit itself. It would be further beneficial if the output result was independent of process and temperature variations.